Time for a new release?

[krassowski]

It's been almost 6 months since the last release and there were 19 commits merged since. I would propose to cut another release, possibly after first merging a few more PRs. I looked through the recent PRs and think these appear ready and hopefully uncontroversial:

• Validate extension name before toggling through CLI #1509
• display_url: Don't duplicate public_url and local_url if they are the same #1494
• Allow ServerApp.no_browser_open_file option to be set via config #1501

I brought this up towards the end of the jupyter-server call and there were no objections.